Study detail and analysis, Parke-Davis 945-295

This 7-week randomized, double-blind trial compared the efficacy of gabapentin 1800 mg/day, and 2400 mg/day to placebo for the treatment of post-herpetic neuralgia. The "fixed-dose parallel group" design of this trial was employed to gather data regarding the dose-response effect of gabapentin. The primary efficacy measurement was the change from baseline in the average daily pain rating scores. The pain score was derived from an 11-point Likert scale in which 0 represented "no pain" and 10 represented the "worst pain possible." Results showed that gabapentin-treated patients experienced a statistically significant reduction in the mean pain score from baseline (p<0.01) relative to placebo-treated patients for both the 1800 mg/day and 2400 mg/day groups. The mean reduction in pain score from baseline was -34.5% in the 1800 mg/day gabapentin group, and -34.4% in the 2400 mg/day gabapentin group. Thus, the two dosage groups (while not compared statistically for difference) are clearly similar. Comparing the two gabapentin dosage groups with regard to the clinically relevant "responder rate" (the percentage of patients with a reduction in mean pain score of > 50%) also shows that responses were similar for the 1800 mg/day (32% responder rate) and 2400 mg/day (34% responder rate) groups. Thus, no dose-response effect for gabapentin was found, and this study does not provide substantial evidence of increased efficacy of gabapentin for post-herpetic neuralgia at doses above 1800 mg/day.